1. Field of the Invention
The present invention relates to an endoscope system capable of clearly observing a blood vessel pattern such as a superficial microvessel, a microstructure such as a pit pattern, or an irregular pattern such as hypertrophy, and an image generation method.
2. Description of the Related Art
In recent medical treatment, diagnosis or the like using an endoscope apparatus has been widely performed. In this endoscopic diagnosis, not only normal light observation, in which white light of broadband light is used as illumination light within the subject, but also special light observation, in which a lesion, such as cancer, is made clearer than other parts or the position or the size of the lesion is easily intuitively grasped by using the special light having a specific wavelength as illumination light, is performed.
For example, in JP2001-170009A, using the fact that the degree of penetration in the depth direction of the body tissue and the absorption characteristics of hemoglobin in the blood have a wavelength dependency, a microstructure such as a pit pattern or a microvessel formed in a body tissue surface layer is made clear with blue narrow-band light having a short wavelength, and a thick blood vessel located in a medium-deep layer of the body tissue is made clear with green narrow-band light having a longer wavelength than that of the blue narrow-band light. Blood vessels or superficial microstructures of the surface to medium-deep layers are important clues at the time of differential diagnosis of cancer or degree-of-penetration diagnosis. Therefore, it is possible to greatly improve the accuracy of differentiation and the like by making the blood vessels or the superficial microstructures of the surface to medium-deep layers clear using blue narrow-band light or green narrow-band light.
In addition, in JP1996-252218A (JP-H08-252218A), a boundary between a lesion part and a normal part is made clear by using the characteristic that the amount of auto-fluorescence emitted from the lesion part, which is thickened due to the lesion such as cancer, is less than the amount of auto-fluorescence from the normal part, which is not thickened, when irradiating the body tissue with excitation light for exciting the auto-fluorescence. By making the boundary between the lesion part and the normal part clear as described above, it becomes easy to grasp the position or the size of the lesion part when performing observation from a distant-view state as at the time of screening.